When the data on the TMP time course were fit to a linear regression, each system was found to perform differently. Data from the membranes in which a US frequency of 20 kHz was applied showed the best fit to a linear regression (Table 1). Coefficients of the regression (Table 1) showed the higher initial TMP values, but the positive value of the slope indicated that membrane fouling was not only controlled, but also reduced. For 25 and 30 kHz, the trend of the data was similar. No linear fit was achieved, but in both cases the slope registered a negative value, signifying a progressive fouling of the membrane. The data found for the system working with 40 kHz can be considered anomalous. Linear fit was non-existent with continuous falls in TMP.

Table 1

Frequency . | Average . | TMP_{min}
. | TMP_{max}
. | r^{2}
. | Slope (a) . | (b) . |
---|---|---|---|---|---|---|

20 kHz | −0.052 | −0.028 | −0.068 | 0.645 | 4 × 10^{−4} | −0.072 |

25 kHz | −0.073 | −0.031 | −0.099 | 0.211 | −1 × 10^{−4} | −0.060 |

30 kHz | −0.067 | −0.046 | −0.086 | 0.177 | −2 × 10^{−4} | −0.063 |

40 kHz | −0.050 | −0.016 | −0.079 | 0.031 | 3 × 10^{−5} | −0.054 |

Frequency . | Average . | TMP_{min}
. | TMP_{max}
. | r^{2}
. | Slope (a) . | (b) . |
---|---|---|---|---|---|---|

20 kHz | −0.052 | −0.028 | −0.068 | 0.645 | 4 × 10^{−4} | −0.072 |

25 kHz | −0.073 | −0.031 | −0.099 | 0.211 | −1 × 10^{−4} | −0.060 |

30 kHz | −0.067 | −0.046 | −0.086 | 0.177 | −2 × 10^{−4} | −0.063 |

40 kHz | −0.050 | −0.016 | −0.079 | 0.031 | 3 × 10^{−5} | −0.054 |

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